1. Field of the Invention
The present invention relates to a method of and device for detecting displacement of paper sheets in transit by a device which transports the paper sheets and stacks them according to the classification of the sheets.
2. Description of the Prior Art
In recent years, devices have been put into practical use which manage to sort out paper sheets such as bank-notes, checks, and stock certificates and stack them in prescribed numbers according to their classifications. Such a device, for example, a bank-notes sorter, works as follows. When bank-notes are set in a supply unit of the machine, a picker thereof picks up bank-notes one by one from the supply unit and places it on a conveyer belt. During conveyance, the inspection unit of the machine examines prescribed items about the bank-notes as well as counts their number. At the terminus of the conveyer system, a classifying gate and a stacking device segregate the bank-notes according to the kinds and pile them up in prescribed numbers at the stacking unit, based on the results of the inspection and counting.
In the bank-notes sorter described in the above, the final object is that the classification and stacking of the bank-notes are achieved with high reliability by carrying out accurate inspection and counting at the inspection unit. Therefore, displacement (referred to as "card skew" hereinafter) or off-centering (referred to as "card shift" hereinafter) of the bank-note at the inspection unit is undesirable due to the fact that it tends to reduce the reliability of the device. Moreover, even if the displacement or shift of the bank-note was checked accurately at the inspection unit, the bank-note might still undergo a displacement subsequent to completion of inspection and counting before it reaches the classifying gate. In such a case, paper clogging at the classifying gate, might appear, preventing the machine from achieving the precise piling-up of the bank-notes in spite of the accurate inspection and counting. In addition, in case the distance between the bank-notes in transit is not large enough, the speed of classification of the bank-notes at the classifying gate cannot follow the rate of accumulation of the notes there. This makes; it impossible to have a precise piling-up of the bank-notes due to paper clogging and the like at the gate. Consequently, for precise inspection of the operation of the bank-notes sorter, a checking of the transporting distance, displacement, and shift of the notes is required with due consideration on their mutual relationship.
As a device which is capable of performing such a check on operation of the bank-notes sorter, it is conceivable, for example, to apply a displacement detection device with a sensor that can detect the position of the edges of the paper sheets, as shown in Japanese Patent Publication No. 118605/1981 filed by the present applicant. With this displacement detection device, an accurate displacement detection of the bank-notes on real time is performed while they are being transported. On the other hand, an attempt to apply the displacement detection device to the operation check of the bank-notes sorter faces the following difficulties. Namely, because the sensor for obtaining the information on the edges of the paper sheets is arranged in the same direction as that of the conveyance of the paper sheets, the size of the displacement detector has to correspond to the length of the paper sheets, resulting in a large dimension of the structure. Because of this, for a conveyer stream with a complex mesh of belts, the displacement detector can be installed only at specially restricted spots so that the adjustment of the bank-notes sorter is usually time-consuming and its fine adjustment is often impossible.